The present invention, in some embodiments thereof, relates to a planar stator and, more particularly, but not exclusively, to a stator for an axial air-gap electric machine such as a motor and/or a generator.
Prior art brushless axial gap electric machines which incorporate planar stators typically comprise windings comprising either separated coils or entire-phase coil chains. In both cases, the active winding conductor sections occupy only a part of a disk-shaped volume defined by the planar structure of the stator, since the winding design does do not allow for overlapping of wound components.
U.S. Pat. No. 4,336,475 to Shigeki Morinaga et al. discloses a poly-phase multi-layer planar winding made of separated triangular coils. The stator volume utilization efficiency may be about 50% since about half of volume both inside and outside of the coils is not used.
US patent application 2010/0253173A1 by Koji Miyata et al discloses a single-phase single-layer planar winding made of separated triangular coils embedded into solid construction. The stator volume utilization efficiency may be about 50% since about half of volume both inside and outside of coils is not used.
US patent application 2010/0295316A1 by Derek Grassman discloses a single-phase single-layer planar winding made of separated triangular coils embedded into solid construction. The stator volume utilization efficiency may be about 67% since about one-third of volume inside of coils is not used.
US patent application 2008/000678833A1 by Peter D. Witt discloses a three-phase two-layer planar winding made of three half-circle coil chains stacked and glued to each other. Stator volume utilization efficiency in this case may also be about 50%, since about half of volume inside of coils is not used.
U.S. Pat. No. 7,084,548B1 to Chrystopher W. Gabrys discloses a 3-phase single-layer NON-planar winding made of separated coils. The stator volume utilization efficiency may be about 100%, but the stator disclosed by Gabrys is not planar and therefore has inherent functional disadvantages, including the fact that such stators cannot efficiently be stacked face-to-face with other stators in multi-stator designs, cannot easily be used in modular multi-stator/rotor electric machines, and impose limitations on compatible rotor designs.
U.S. Pat. No. 4,476,409 to Tadashi Fukami discloses 3-phase cup-like windings. The stator volume utilization efficiency may be about 100%, but such stators also are non planar and may efficiently be used only in single-stator single-module electric machines.
US patent application 2010/0117481A1 by Matthew Greaves et al discloses a 3-phase double-layer non-planar winding made of twisted phase conductors. The stator volume utilization efficiency may be about 100%, but this stator also is not planar, and therefore also has the inherent functional disadvantages of the non-planar stator designs mentioned above.